Processes are known for manufacturing of cellular shades, in which the body of the shade consists of a number of identical fabric strips, folded and adhesively-bonded to one another so as to define cells. Typically, the cells extend transversely, but they may also be arranged vertically, or at an angle to the horizontal. When the shade is raised, the cells are collapsed; when the shade is lowered, the cells expand. Such shades contain essentially static masses of air, and thus provide useful thermal insulation.
Conventionally, such shades are manufactured by creasing strips of fabric lengthwise to define cell precursors, and using a liquid adhesive to bond tabs thus formed on each successive strip to the central body portion of the next strip, completing the cells. U.S. Pat. No. 4,450,027 to Wendell B. Colson shows a method of and apparatus for making such shades from continuous fabric strip material. The adhesive bonding techniques employed heretofore in the manufacture of such shades have typically involved the positioning of beads of suitable adhesive on either the tabs or the central body portion of the next strip.
Other patents show related techniques. For example, U.S. Pat. Nos. 4,677,013, 4,685,986, 4,631,217, 4,677,012, and 4,676,855, all to Richard N. Anderson, show further methods of manufacture of cellular shades. For example, the strips may be creased to take a Z-shape, and tabs on either side of the strip are adhesively bonded to the prior and successive strips to form the completed shade structure. See also U.S. Pat. No. 4,732,630 to Schnebly, and U.S. Pat. No. 4,849,039 to Colson and Swiszcz.
All of these patents and applications thus teach adhesive bonding of tabs formed on a strip of material to a preceding strip using a liquid adhesive, or in some cases to both preceding and successive strips, to form the cells. This technique is the most practical known, but has effectively limited the types of fabrics from which such shades can be made. Specifically, the material comprising the shade is normally stacked with the cells in the collapsed position while the liquid adhesive cures. In this position, the adhesive on the tabs of each strip is normally juxtaposed to the strip from which the tabs are formed, as well as the strips to which the tabs are to be bonded. Accordingly, the fabrics have had to have been selected such that the adhesive does not penetrate the fabric, so that the tabs from a first strip do not adhere to the strip from which they are formed, but only to the strips to which they are to be bonded; i.e., so that the interiors of the cells are not bonded closed.
This limitation on the method of forming shades shown in the patents mentioned above has been such that certain highly desirable "sheer" fabrics have not been usable. "Sheer" as used in this specification refers to fabrics which are highly translucent or are substantially transparent to visible light. Such sheer fabrics are normally relatively open weave, and are typically woven or knit of monofilament thread. When a bead of conventional adhesive sufficient to form a good bond when employed to form cellular blinds of typical non-sheer materials is placed on these open-weave sheer fabrics, the adhesive tends to penetrate the fabric, particularly if pressure is exerted thereon to ensure a good bond. Thus, if sheer materials are used in the normal manufacturing process, the inner walls of the cells tend mutually to adhere, which ultimately prevents the blind from opening properly. This difficulty has in fact prevented manufacture of cellular shades of sheer materials, especially fabrics, permeable to liquid adhesives, which would be highly desirable to many consumers.
Various methods have been tried for adhesive manufacture of such cellular shades using sheer materials. Bands of heavier material have been knit into the sheer material at the locations where the adhesive is applied, to slow passage of the adhesive therethrough. In most cases this material was very difficult to handle and roughly twice as expensive as the plain sheer material. Using a more viscous adhesive which does not penetrate the fabric also has proven unsatisfactory.
It appears that successful adhesive bonds between open-weave sheer fabrics, particularly those knit or woven of monofilament materials, require impregnation and solidification of the adhesive, wherein the adhesive actually penetrates through the fabric and then solidifies into a more or less solid mass encapsulating the fibers. If the adhesive is made too viscous it cannot penetrate the fabric. This is less of a problem with tightly woven conventional fabrics, wherein the fibers normally have many small "hairy" sub-fibers, which provide sufficient surface area to which the adhesive adheres that a good bond can be formed without encapsulation. To a considerable extent adhesives which do not permeate the fabric have been successfully employed to form cellular shades, e.g. according to the Colson and other patents discussed above, of opaque, non-sheer fabrics. Openweave sheer fabrics do not provide sufficient surface area to allow formation of a strong non-impregnating bond. Particularly where the fabric is knit or woven of monofilament thread which is not "hairy", the impregnation mode of adhesion is required to form an effective bond. In either case, when the impregnation occurs, the tabs tend to be bonded to both their own and the preceding and/or successive strips, preventing the blind from opening properly.
U.S. Pat. No. 4,673,600 also to Richard N. Anderson addresses this problem. According to this patent, sheer materials can be formed into "honeycomb" or cellular shades and adhesively bonded by allowing the adhesive to cure while the cells are in the expanded state. This method is useful if quick-setting adhesives, e.g. hot melt adhesives, are used. However, this method poses certain constraints on the design of the cellular shade thus manufactured, and on the manufacturing processes employed.